Photographic products and processes comprising synthetic nuclear isotopes

ABSTRACT

Photosensitive silver halide emulsions having increased photographic sensitivity are prepared by incorporating therein a nuclear radiation source.

United States Patent n91 Gerber et al.

[ Dec.3,1974

[ PHOTOGRAPHIC PRODUCTS AND PROCESSES COMPRISING SYNTHETIC NUCLEAR ISOTOPES [75] Inventors: Arthur M. Gerber, Boston; Vivian K. Walv'vorth, Concord, both of Mass.

[73] Assignee: Polaroid Corporation, Cambridge,

' Mass.

[22] Filed: May 11, 1972 [21] App]. No.: 252,270

[52] US. Cl...., 96/94 1R, 96/108, 250/65 R,

250/65 F [51] Int. Cl G030 1/02, G03c 1/28 [58] Field of Search. 96/45.2, 107, 108, 94 R;

250/106 R, 65 F, 65 R Primary Examiner--Norman G, Torchin Assistant Examiner-Alfonso T. Suro Pico Attorney, Agent, or Firm-Philip G. Kiely 5 7 ABSTRACT Photosensitive silver halide emulsions having in-.

creased photographic sensitivity are prepared by incorporating therein a nuclear radiation source.

25 Claims, N0 Drawings PHOTOGRAPHIC PRODUCTS AND PROCESSES COMPRISING SYNTHETIC NUCLEAR ISOTOPES BACKGROUND-OF THE INVENTION Photographic sensitivity or speed of silver halide emulsions is enhanced by preexposing the emulsion to electromagnetic radiation. Such a procedure is especially employed by astronomers and spectrographers who find it necessary to achieve sensitivity unavailable in the basic emulsion.

The aforementioned pre-exposure is generally applied to a cast emulsion layer, that is, an emulsion carried on a support, a conventional negative. This procedure, however, does not result in a homogeneous exposure of the grains by the incident light. The exposing light emanates from a source such as an incandescent lamp or a fluorescent lamp of some type, thus introducing a geometry into the system which contributes to the lack of homogeneity of exposure. Factors such as depth of the emulsion and alignment of silver halide grains in the emulsion will cause a greater degree of exposure to occur with the grains lying nearer the surface than those deeper in the layer or those shielded to any degree by overlying silver halide grains.

In addition, the process of pre-exposureitself, i.e., duration and quanta of exposure, is fairly critical since the fog level of the emulsion must not be exceeded'or the emulsion will be rendered substantially useless. On the other hand, sufficient minimum exposure must be given to achieve any increase in sensitivity.

A novel method for pre-exposing photosensitive silver halide emulsions has now been found which is not susceptible to the deficiencies of the prior art.

BRIEF DESCRIPTION OF THEINVENTION DETAILED DESCRIPTION OF THE INVENTION By means of the present invention, it has now been found that enhanced photographic response of silver halide grains can be achieved by uniformly disposing in the emulsion a nuclear radiation source, preferably one of relatively short half life. By disposing a nuclear radiation source in a silver halide emulsion, the emulsion can be conveniently mixed or stirred to provide a uniform dispersion of the nuclear radiation source within the emulsion, thus insuring uniform interaction with substantially all the silver halide grains. Thus, the geometry of the source, the location of the individual silver halide grains and the depth of the emulsionlayer clear radiation as employed herein is intended to refer to products emitted as a result of the decay of the nucleus.

Suitable nuclear radiation sources are well known to the art and are commercially available. Particularly preferred nuclear radiation sources which are commercially available are technetium-99m (0.14 mev gamma, half life 6 hours) and indium-l 13m (039 mev gamma half life 1.7 hours). Other suitable sources include isotopes of silver, bromine, chlorine and iodine. Thus, the compounds employed in forming the silver halide grains could themselves comprise nuclear radiation sources. As well as the foregoing, isotopes of other elements may be employed.

The employment of a nuclear radiation source for sil ver halide grain treatment provides a highly quantita tive and precise control over the degree of hypersensi- ...tizatio n .of the emulsion. By employing'a combination of conventional radiation detection techniques, e.g., scintillation counting, with photographic sensitometry, it is possible to control accurately the amount of nuclear radiation source employed to provide an emulsion with the desired degree of treatment, for example, obtained at a level just below that which would produce visible photographic fogging.

The amount and nature of nuclear radiation source incorporated into photographic emulsions may vary depending upon the type of emulsion and speed and stability desired. A relatively short lived isotope (half life less than 1 day) is preferred in the present invention because an emulsion treated with said isotope could be handled without special precautions after overnight storage, for example. In addition, short half life corresponds to a relatively high specific activity, thus permitting extremely small quantities, in some cases, submicrogram quantities, of the source to provide the desired effect. Advantageous results have been achieved using 0.01 to 1.0 millicuries of nuclear radiation source per gram of silver.

While a relatively short-lived source is preferred, it should be understood that a source with a relatively long half life may also be employed. However, the employment of such an isotope requires that it subsequently be removed from the emulsion or the emulsion placed in storage until the radioactivity produced by the emitter is sufficiently dissipated to permit normal handling and use.

The nuclear radiation source may be provided to the silver halide emulsion at any point prior to casting the emulsion layer. Preferably, it is added prior to the ripening stage. Thus the addition and mixing of the emulsion with the nuclear radiation source disposed therein substitutes for a ripening step. The radiation source selected should not be one which deleteriously affects the photographic properties of the emulsion. The residue of the source should either be substantially innocuous are all eliminated as factors which could contribute to with respect to the photographic properties of the emulsion or present in a sufficiently small quantity so that any effect will be minimal. Alternatively, if the residue or daughter product is not incorporated in the silver halide crystals, it could be removed by washing the emulsion. Generally, since a satisfactory degree of exposure is achieved with extremely low level of nuclear radiation source, the residue can be left in the emulsion without deleteriously affecting the emulsion.

The following non-limiting examples illustrate the novel processes of the present invention.

EXAMPLE I A silver iodochlorobromide emulsion (12 percent silver. 11 percent gelatin) was split into two 80 ml. portions wherein half was left unsensitized and the other half was gold sensitized by the addition of gold thiocyanate. Incorporated into each emulsion was 1.0 millicuries of indium-1 13m which was eluted from a column of tin-113 with 0.05N hydrochloric acid. The column was an isotope generator commercially available from New England Nuclear Corporation, Boston, Massachusetts. The emulsions were then stirred for 16 hours with a magnetic stirrer. Control samples, prepared in the same manner except for the addition of the indium 1 13m, and the emulsions of the present invention were then coated on a support according to the same procedure and exposed to a conventional density step wedge and processed with a processing solution and an imagereceiving element from a Type 42 film assembly (Polaroid Corporation, Cambridge, Massachusetts). The negative and image-receiving elements were maintained in superposition for 15 seconds after which they were stripped apart. The emulsions of the present invention showed increased latitude and speed and decreased contrast in comparison with the control. An even greater increase in photographic sensitivity was achieved with the sample which had not been sensitized with gold than with the sample that had been sensitized with gold. Similar advantages were achieved when the emulsions were processed in a conventional manner employing Dektol (Eastman Kodak Company, Rochester, New York) as the developer.

As stated above, the nuclear radiation source may be disposed in the emulsion at any time prior to casting the emulsion on a support. It should be understood that this includes forming the emulsion in the presence of the nuclear radiation source. Thus, it is the intent of the present invention that the nuclear radiation source be incorporated into the emulsion at any time during the preparation of the emulsion.

In a particularly preferred embodiment, the silver halide grains are formed in the presence of the nuclear radiation source. Particularly advantageous results have been achieved employing this method. For example, it is noted that ripening time can be decreased by a factor of almost as compared with a control emulsion preparation. In addition, it is believed that by forming the silver halide grains in the presence of the nuclear radiation source, dislocations in the grain lattice occur during the grain growing step, thus providing a greater effect than that achieved by surface effect sensitization.

The following non-limiting example illustrates the formation of silver halide grains in the presence of a nuclear radiation source.

EXAMPLE II To a reaction vessel was added 681.9 g. of water, 11.4 g. potassium bromide, 6.9 g. potassium iodide, 208.8 g. phthaloated gelatin and 6.3 g. of a solution of 6.0 MG of indium-113m in 0.05N hydrochloric acid. The contents of the vessel were mixed to dissolve and then over a period of 12 minutes and 28 seconds at a flow rate of 58.9 milliliters per minute and a reaction vessel temperature of 68 C. was added 735.0 milliliters each of 1N silver nitrate and 1N potassium bromide simultaneously by means of constant flow titration. The temperature was then very slowly lowered to room temperature overnight under agitation. The mixture was then chilled to about 15 C. and 10 percent sulfuric acid was added slowly until the pH was about 2.5. The thus-flocculated gelatin silver bromide emulsion was washed with chilled water until the conductivity of the supernatant liquid dropped below micromho per centimeter. The emulsion was then heated to about 38+ C. and 10 percent sodium hydroxide was added slowly to raise the pH to about 6.0 to redissolve the emulsion. The emulsion was then heated to 51 C. and a gold thiocyanate ripening agent was added. The emulsion was then coated on a support after 0, 60, and 210 minutes of ripening (after addition of gold thiocyanate) and exposed using a sensitometer. Processing was accomplished with a Type 42 processing reagent and receiving element as described in Example I.

A control was prepared employing the same procedure as above except that the indium-1 13m employed had been allowed to decay overnight to indium-113 prior to addition to the reaction vessel.

In the control emulsion 210 minutes was required for optimum ripening, whereas optimum ripening time for the emulsion of the present invention was found to be 60 minutes. In addition greater speed and dynamic range was achieved by means of the present invention.

While not intending to be bound by any theory, it is believed that the nuclear radiation source produces, by its decay and emissions, physical and/or chemical alterations in the silver halide lattice. These alterations could serve as electron traps and ultimately as sites for latent image specks. Reduced silver along the track of radiation may further increase the quantum efficiency by lowering the number of photolytic silver atoms needed to form a latent image center. It is believed that the addition of the nuclear radiation source subsequent to grain formation effects a prefogging or homogeneous preexposure of the grains.

The specific composition or method of preparation of silver halide emulsions suitable for use in the present invention is not critical to the operation of the present invention. For example, the present invention may be employed in preparing emulsions for wet processing, emulsions employed in diffusion transfer processing and direct positive emulsions.

In the production of the photosensitive silver halide emulsions suitable for employment in the present invention, the silver halide crystals may be prepared by reacting a water-soluble silver salt, such as silver nitrate, with at least one water-soluble halide, such as ammonium, potassium or sodium bromide, preferably together with a corresponding iodide, in an aqueous solution of a peptizing agent such as a colloidal gelatin solution; digesting that dispersion at an elevated temperature, to provide increased crystal growth; washing the resultant water-soluble salts by chilling the dispersion, noodling the set dispersion, and washing the noodles with cold water, or alternatively, employing any of the various flocculation systems, or procedures, adapted to effect removal of undesired components, for example, the procedures described in US. Pat. Nos. 2,614,928; 2,614,929; 2,728,662; and the like; after-ripening the dispersion at an elevated temperature in combination priate dispersing solvent such as methanol, ethanol, ac-

etone, water, and the like; all according to the traditional procedures of the art, as described in Hamer, F. M., The Cyanine Dyes And Related Compounds.

Additional optional additives, such as coating aids, hardeners, viscosity-increasing agents, stabilizers, preservatives, and the like, for example, those set forth hereinafter, also may be incorporated in theemulsion formulation, according to the conventional procedures known in the photographic emulsion manufacturing art.

The photoresponsive material of the photographic emulsion will, as previously described, preferably comprise a crystal of a silver compound, for example, one or more of the silver halides such as silver chloride, silver iodide, silver bromide, or mixed silver halides such as silver chlorobromide, silver chloroiodobromide or silver iodobromide, of varying halide ratios and varying silver concentrations.

What is claimed is:

l. The method for enhancing photographic sensitivity of a silver halide emulsion which comprises disposing a nuclear radiation source in the silver halide emulsion prior to casting a layer of said emulsion in an amount sufficient to provide sufficient interaction with the silver halide grains to provide said enhanced sensitivity.

.2. The method as defined inclaim 1 wherein said source comprises an alpha emitter.

3. The method as defined in claim 1 wherein said source comprises a beta emitter.

4. The method as defined in claim 1 wherein said source comprises a gamma emitter.

5. The method as defined in claim 1 wherein said source comprises a beta and gamma emitter.

6. The method as defined in claim 1 wherein said source is added just prior to coating said emulsion on a support.

7. The method as defined in claim 1 wherein said source is added to the emulsion prior to ripening the emulsion. v

8. The method as defined in claim 1 which includes the step of removing the residue of the nuclear radiation source from said emulsion.

9. The method as defined in claim 4 wherein said gamma source comprises indium-1 13m.

10. The method as defined in claim 1 wherein sufficient nuclear radiation source is added to said emulsion to expose the silver halide grains in said emulsion to a subthreshold fog level.

11. The method as defined in claim 1 wherein said nuclear radiation source has a half life of less than 6 hours.

12. The method as defined in claim 11 wherein said nuclear radiation source is added at a level of between .about 0.01 and 1.0 millicuries per gram of silver.

13. A product which comprises a photosensitive silver halide emulsion having a residue therein from the decay of a synthetic nuclear isotope having a half life of less than 1 day.

14. The product as defined in claim 13 wherein said source comprises an alpha emitter.

15. A product as defined in claim 13 wherein said source comprises a beta emitter.

16. A product as defined in claim 13 wher'ein said source comprises'a gamma emitter. I

17. A product as defined in claim 13 wherein said source comprises a beta and a gamma emitter.

18. A product as defined in claim 16 wherein said residue is indium-l 13m.

19. A method for preparing a photosensitive silver halide emulsion which comprises reacting a, water soluble silver salt with at least one water soluble halide in the presence of a nuclear radiation source in an amount sufficient to provide enhanced photograpahic sensitivity by interaction with the silver halide grains.

20. The method as defined in claim 19 wherein said source is an alpha emitter.

21. The method as defined in claim 19 wherein said source is a beta emitter. t

22. The method as defined in claim 19 wherein said source is a gamma emitter. 1

23. The method as defined in claim 19 wherein said source comprises a beta and a gamma emitter.

24. The method as defined in claim 22 wherein said gamma emitter is indium113m.

25. The product which comprises a photosensitive silver halide emulsion containing a nuclear radiation 

1. THE METHOD FOR ENHANCING PHOTOGRAPHIC SENSIVITY OF A SILVER HALIDE EMULSION WHICH COMPRISES DISPOSING A NUCLEAR RADIATION SOURCE IN THE SILVER HALIDE EMULSION PRIOR TO CASTING A LAYER OF SAID EMULSION IN AN AMOUNT SUFFICIENT TO PROVIDE SUFFICIENT INTERACTION WITH THE SILVER HALIDE GRAINS TO PROVIDE SAID ENHANCED SENSIVITY.
 2. The method as defined in claim 1 wherein said source comprises an alpha emitter.
 3. The method as defined in claim 1 wherein said source comprises a beta emitter.
 4. The method as defined in claim 1 wherein said source comprises a gamma emitter.
 5. The method as defined in claim 1 wherein said source comprises a beta and gamma emitter.
 6. The method as defined in claim 1 wherein said source is added just prior to coating said emulsion on a support.
 7. The method as defined in claim 1 wherein said source is added to the emulsion prior to ripening the emulsion.
 8. The method as defined in claim 1 which includes the step of removing the residue of the nuclear radiation source from said emulsion.
 9. The method as defined in claim 4 wherein said gamma source comprises indium-113m.
 10. The method as defined in claim 1 wherein sufficient nuclear radiation source is added to said emulsion to expose the silver halide grains in said emulsion to a subthreshold fog level.
 11. The method as defined in claim 1 wherein said nuclear radiation source has a half life of less than 6 hours.
 12. The method as defined in claim 11 wherein said nuclear radiation source is added at a level of between about 0.01 and 1.0 millicuries per gram of silver.
 13. A product which comprises a photosensitive silver halide emulsion having a residue therein from the decay of a synthetic nuclear isotope having a half life of less than 1 day.
 14. The product as defined in claim 13 wherein said source comprises an alpha emitter.
 15. A product as defined in claim 13 wherein said source comprises a beta emitter.
 16. A product as defined in claim 13 wherein said source comprises a gamma emitter.
 17. A product as defined in claim 13 wherein said source comprises a beta and a gamma emitter.
 18. A product as defined in claim 16 wherein said residue is indium-113m.
 19. A method for preparing a photosensitive silver halide emulsion which comprises reacting a water soluble silver salt with at least one water soluble halide in the presence of a nuclear radiation source in an amount sufficient to provide enhanced photograpahic sensitivity by interaction with the silver halide grains.
 20. The method as defined in claim 19 wherein said source is an alpha emitter.
 21. The method as defined in claim 19 wherein said source is a beta emitter.
 22. The method as defined in claim 19 wherein said source is a gamma emitter.
 23. The method as defined in claim 19 wherein said source comprises a beta and a gamma emitter.
 24. The method as defined in claim 22 wherein said gamma emitter is indium-113m.
 25. The product which comprises a photosensitive silver halide emulsion containing a nuclear radiation source. 